Assembly of chemically modified protein nanocages into 3D materials for the adsorption of uremic toxins.

Hemodialysis fails to remove protein-bound uremic toxins that are attributed with high cardiovascular risk. Application of adsorption materials is a viable strategy, but suitable biocompatible adsorbents are still not available. Here, we demonstrate that adsorbents based on the bottom-up assembly of the intrinsically biocompatible protein cage ferritin are applicable for toxin adsorption. Due to the size-exclusion effect of its pores, only small molecules such as uremic toxins can enter the protein cage. Protein redesign techniques that target selectively the inner surface were used to introduce anchor sites for chemical modification. Porous crystalline adsorbents were fabricated by bottom-up assembly of the protein cage. Linkage of up to 96 phenylic or aliphatic molecules per container was verified by ESI-MS. Materials based on unmodified ferritin cages can already adsorb the uremic toxins. The adsorption capacity could be increased by about 50% through functionalization with hydrophobic molecules reaching 458 µg g-1 for indoxyl sulfate. The biohybrid materials show no contamination with endotoxins and do not activate blood platelets. These findings demonstrate the great potential of protein-based adsorbents for the clearance of uremic toxins: modifications enhance toxin adsorption without diminishing the biocompatibility of the final protein-based material.

Chemokine CCL9 Is Upregulated Early in Chronic Kidney Disease and Counteracts Kidney Inflammation and Fibrosis.

Inflammation and fibrosis play an important pathophysiological role in chronic kidney disease (CKD), with pro-inflammatory mediators and leukocytes promoting organ damage with subsequent fibrosis. Since chemokines are the main regulators of leukocyte chemotaxis and tissue inflammation, we performed systemic chemokine profiling in early CKD in mice. This revealed (C-C motif) ligands 6 and 9 (CCL6 and CCL9) as the most upregulated chemokines, with significantly higher levels of both chemokines in blood (CCL6: 3-4 fold; CCL9: 3-5 fold) as well as kidney as confirmed by Enzyme-linked Immunosorbent Assay (ELISA) in two additional CKD models. Chemokine treatment in a mouse model of early adenine-induced CKD almost completely abolished the CKD-induced infiltration of macrophages and myeloid cells in the kidney without impact on circulating leukocyte numbers. The other way around, especially CCL9-blockade aggravated monocyte and macrophage accumulation in kidney during CKD development, without impact on the ratio of M1-to-M2 macrophages. In parallel, CCL9-blockade raised serum creatinine and urea levels as readouts of kidney dysfunction. It also exacerbated CKD-induced expression of collagen (3.2-fold) and the pro-inflammatory chemokines CCL2 (1.8-fold) and CCL3 (2.1-fold) in kidney. Altogether, this study reveals for the first time that chemokines CCL6 and CCL9 are upregulated early in experimental CKD, with CCL9-blockade during CKD initiation enhancing kidney inflammation and fibrosis.

Prevention of vascular calcification by the endogenous chromogranin A-derived mediator that inhibits osteogenic transdifferentiation.

The adrenal glands participate in cardiovascular (CV) physiology and the pathophysiology of CV diseases through their effects on sodium and water metabolism, vascular tone and cardiac function. In the present study, we identified a new adrenal compound controlling mesenchymal cell differentiation that regulates osteoblastic differentiation in the context of vascular calcification. This peptide was named the "calcification blocking factor" (CBF) due to its protective effect against vascular calcification and is released from chromogranin A via enzymatic cleavage by calpain 1 and kallikrein. CBF reduced the calcium content of cells and thoracic aortic rings under calcifying culture conditions, as well as in aortas from animals treated with vitamin D and nicotine (VDN animals). Furthermore, CBF prevented vascular smooth muscle cell (VSMC) transdifferentiation into osteoblast-like cells within the vascular wall via the sodium-dependent phosphate transporter PIT-1 and by inhibition of NF-κB activation and the subsequent BMP2/p-SMAD pathway. Pulse pressure, a marker of arterial stiffness, was significantly decreased in VDN animals treated with CBF. In line with our preclinical data, CBF concentration is significantly reduced in diseases characterized by increased calcification, as shown in patients with chronic kidney disease. In preparation for clinical translation, the active site of the native 19-AS long native CBF was identified as EGQEEEED. In conclusion, we have identified the new peptide CBF, which is secreted from the adrenal glands and might prevent vascular calcification by inhibition of osteogenic transdifferentiation. The anti-calcific effects of CBF and short active site may therefore promote the development of new tools for the prevention and/or treatment of vascular calcification.

Uremic Toxins Affecting Cardiovascular Calcification: A Systematic Review.

Cardiovascular calcification is highly prevalent and associated with increased morbidity in chronic kidney disease (CKD). This review examines the impact of uremic toxins, which accumulate in CKD due to a failing kidney function, on cardiovascular calcification. A systematic literature search identified 41 uremic toxins that have been studied in relation to cardiovascular calcification. For 29 substances, a potentially causal role in cardiovascular calcification was addressed in in vitro or animal studies. A calcification-inducing effect was revealed for 16 substances, whereas for three uremic toxins, namely the guanidino compounds asymmetric and symmetric dimethylarginine, as well as guanidinosuccinic acid, a calcification inhibitory effect was identified in vitro. At a mechanistic level, effects of uremic toxins on calcification could be linked to the induction of inflammation or oxidative stress, smooth muscle cell osteogenic transdifferentiation and/or apoptosis, or alkaline phosphatase activity. For all middle molecular weight and protein-bound uremic toxins that were found to affect cardiovascular calcification, an increasing effect on calcification was revealed, supporting the need to focus on an increased removal efficiency of these uremic toxin classes in dialysis. In conclusion, of all uremic toxins studied with respect to calcification regulatory effects to date, more uremic toxins promote rather than reduce cardiovascular calcification processes. Additionally, it highlights that only a relatively small part of uremic toxins has been screened for effects on calcification, supporting further investigation of uremic toxins, as well as of associated post-translational modifications, on cardiovascular calcification processes.

Development, establishment and validation of in vitro and ex vivo assays of vascular calcification.

OBJECTIVE: Vascular calcification (VC) is one major complication in patients with chronic kidney disease, with a misbalance in calcium and phosphate metabolism playing crucial role. The mechanisms underlying VC have not been entirely revealed to date. As studies aiming at the identification and characterization of the involved mediators are highly relevant, we developed a standardized operating protocol for in vitro and ex vivo approaches in this study to aiming at the comparability of these studies. APPROACH AND RESULTS: We analyzed in vitro and ex vivo experimental conditions to study VC. Therefore, vascular smooth muscle cells were used for in vitro experiments and rat aorta for ex vivo experiments. The degree of calcification was estimated by quantification of calcium concentrations and by von Kossa staining. As a result, a step-by-step protocol for performing experiments on VC was established. We were able to demonstrate that the degree and the location of VC in vascular smooth muscle cells and aortic rings was highly dependent on the phosphate and CaCl2 concentration in the medium as well as the incubation time. Furthermore, the VC was reduced upon increasing fetal calf serum concentration in the medium. CONCLUSION: In the current study, we developed and validated a standardized operating protocol for systematic in vitro and ex vivo analyses of medial calcification, which is essential for the comparability of the results of future studies.

Sample preparation of formalin-fixed paraffin-embedded tissue sections for MALDI-mass spectrometry imaging.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MALDI MSI) has become a powerful tool with a high potential relevance for the analysis of biomolecules in tissue samples in the context of diseases like cancer and cardiovascular or cardiorenal diseases. In recent years, significant progress has been made in the technology of MALDI MSI. However, a more systematic optimization of sample preparation would likely achieve an increase in the molecular information derived from MALDI MSI. Therefore, we have employed a systematic approach to develop, establish and validate an optimized "standard operating protocol" (SOP) for sample preparation in MALDI MSI of formalin-fixed paraffin-embedded (FFPE) tissue sample analyses within this study. The optimized parameters regarding the impact on the resulting signal-to-noise (S/N) ratio were as follows: (i) trypsin concentration, solvents, deposition method, and incubation time; (ii) tissue washing procedures and drying processes; and (iii) spray flow rate, number of layers of trypsin deposition, and grid size. The protocol was evaluated on interday variability and its applicability for analyzing the mouse kidney, aorta, and heart FFPE tissue samples. In conclusion, an optimized SOP for MALDI MSI of FFPE tissue sections was developed to generate high sensitivity, to enhance spatial resolution and reproducibility, and to increase its applicability for various tissue types. This optimized SOP will further increase the molecular information content and intensify the use of MSI in future basic research and diagnostic applications. Graphical Abstract.